1. Field of the Invention
The invention relates to a non-drain differential signal transmission cable and a ground connection structure thereof.
2. Description of the Related Art
In devices to handle high-speed digital signals of several Gbit/s or more, such as a server, a router or a storage device, differential signal transmission is used for signal transmission between devices or substrates (circuit boards) in a device.
The differential signal transmission is conducted such that signals with 180° inverted phases are transmitted through two paired signal conductors and a difference between the signals received on the side of a receiver is synthesized and outputted. Since currents flowing in the pair of signal conductors flow in opposite directions to each other, electromagnetic wave radiated from a transmission line is small. In addition, since noise from outside is equally superposed on the pair of signal conductors, the effect of noise can be cancelled by synthesizing and outputting the difference on the side of the receiver. Due to these reasons, the differential signal transmission is often used for the high-speed digital signal transmission.
As shown in FIG. 16 and FIG. 17 which is a cross sectional view taken on line B-B of FIG. 16, a differential signal transmission cable 160 used for the differential signal transmission has a pair of signal conductors 161, an insulation 162 covering together the pair of signal conductors 161, a shield conductor 163 provided on an outer periphery of the insulation 162 and a sheath 164 provided on an outer periphery of the shield conductor 163.
The shield conductor 163 may be formed by winding a tape with a conductor (a shielding tape) or is formed by covering with a braided strand. In addition, the sheath 164 may be formed by winding an insulating tape or is formed by extrusion coating of resin.
The differential signal transmission cable 160 is a twinax cable which has a pair of signal conductors 161 aligned in parallel and in which a difference in physical length between the pair of signal conductors 161 and attenuation of signal at high frequency are less than a twisted pair cable formed by twisting a pair of signal conductors. In addition, since the shield conductor 163 is provided covering the pair of signal conductors 161, the characteristic impedance is not unstable even if a metal is placed near the cable, and the noise immunity is also high. Due to such advantages, twinax cables are often used for short-distance signal transmission at relatively high speed.
By the way, the differential signal transmission cable 160 does not have a drain wire. Therefore, for connecting the differential signal transmission cable 160 to a substrate 165, after peeling the differential signal transmission cable 160 in a tiered manner, each of the paired signal conductors 161 is connected to a signal line pad 166 on the substrate 165 using a solder 167 while the shield conductor 163 is directly connected, using the solder 167, to a ground pad 170 which is connected to an inner ground layer 168 in the substrate 165 via a through-hole 169.
The related art may include JP-A-2011-90959.